Field of the Invention
The present invention relates to an image reading device that reads the image of a document and acquires image signals, and an image forming device, and more particularly, relates to an image reading device of a stationary reading type in which the image of a document statically placed is read with a reading unit that transfers in a sub-scanning direction, and an image forming device including the image reading device.
Description of Related Art
Conventional devices of this sort are exemplified by Japanese Unexamined Patent Application Publication No. 2001-230895 and Japanese Unexamined Patent Application Publication No. 2010-107825. As for the image reading device disclosed in Japanese Unexamined Patent Application Publication No. 2001-230895, an elongated reading unit extended in a main scanning direction is reciprocated in a sub-scanning direction, thereby reading images of a document. Herein, electric signals between the reading unit, which is a moving body, and a control unit fixed on an immovable case frame are interchanged with a flexible flat cable (hereinafter, also referred to as “FFC”). Also, a bending portion is provided in the FFC so as to cause the reading unit to smoothly transfer without buckling the FFC in the case in which the reading unit is reciprocated.
In Japanese Unexamined Patent Application Publication No. 2001-230895, an attempt is made to absorb excessive tension applied to the FFC by providing two bending portions so as not to apply the excessive tension to the FFC during transfer. Also, in Japanese Unexamined Patent Application Publication No. 2010-107825, the bending portion of the FFC is stored in a concave portion that is formed by digging down a chassis member on the bottom surface of the case frame, thereby alleviating bending stress applied to the bending portion of the FFC at a home position of the reading unit and reducing a repulsive force attributed to the bending of the FFC.
However, according to the invention disclosed by Japanese Unexamined Patent Application Publication No. 2001-230895, when the two bending portions of the FFC are constituted, curvature of each bending portion increases, which leads to an increase in the bending stress applied to the FFC and raises a possibility that the FFC is deteriorated or broken. In contrast, when curvature R is increased so as to reduce the bending stress, an increase in the size of the device is caused. Also, a gap between the reading unit being transferred and the FFC is narrowed in terms of constitution, so that there is a possibility that, when the FFC slightly floats, the FFC is entangled or caught.
In particular, in recent years, the use of illumination units, in which LEDs are employed as a scanner light source, has been increasing steadily. The efficiency of the light emission of LEDs has been improved year by year, and as for the lighting of a multifunction peripheral (MFP) scanner, an LED light conductor method in which a linear light source is formed with a few LEDs by use of an LED light conductor is being in the mainstream, in place of an array method in which a multitude of LEDs are arranged on an elongated substrate. Also, even when the sensitivity of a charge-coupled device (CCD) is enhanced, which leads to reduction in pixel size and the speeding up of a unit scan method in which the CCD and an optical system are integrated, a small-size unit can be constituted, so that the LED light conductor method tends to be adopted even in the MFP scanner that requires speeds.
However, in unit scanning of a high-speed device, the FFC of a shield type is often used for signal transmission as a measure of preventing noise in high-speed signals, and therefore there is a problem in that the thickness of the FFC is increased due to shielding, and flexibility is further deteriorated, and the risk of being broken or caught is increased, compared with a low-speed device.
Also, according to the invention disclosed by Japanese Unexamined Patent Application Publication No. 2010-107825, the risk that the chassis member of the case frame is broken or caught is solved, but there is a problem in that the size of the device is increased in proportion to the volume of the concave portion to be formed.
Accordingly, as a result of conducting various studies, the inventors of the present invention have found that an approach distance for stabilizing the amount of light is required outside image areas in the LED light conductor method, and a space formed for the approach distance is efficiently used as a storage space for the bending portion of the FFC, and that the FFC can be bent with a sufficient space without further increasing the size of the device for the FFC, and the risk that the FFC is broken or caught can be reduced, with regard to the high-speed scanner that necessitates the high-speed signals.